Treatment of oriented crystalline polyester filaments



3,413,797 TREATMENT OF ORIENTED CRYSTALLINE POLYESTER FILAMENTS lRoy Chapman, Harrogate, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain N Drawing. Filed Aug. 18, 1966, Ser. No. 573,181 Claims priority, application Great Britain, Aug. 23, 1965, 36,025/ 65 3 Claims. (Cl. 57-140) ABSTRACT OF THE DISCLOSURE Drawn polyethylene terephthalate filament yarns of high intrinsic viscosity and high tenacity are heat treated by passing them through a fluidized bed of solid particles maintained in the range 240 C.-264 C. in order to reduce shrinkage without undesirably reducing properties such as tenacity, elongation and modulus.

The filaments have the following properties: intrinsic viscosity of 0.85l.00 dl. per gram, tenacity of at least 8 g.p.d. in the form of a yarn of up to 10,000 denier and not more than one turn per inch twist, extension of at least shrinkage of less than 8%, a 2% modulus of at least 80 g.p.d. and a shrinkage force of less than 0.35 g.p.d.

This invention relates to the treatment of oriented crystalline filament yarns made from polyethylene terephthalate.

Filament yarns made from polyethylene terephthalate of high intrinsic viscosity of the order of 0.85-1.00 dl. per gram have after melt spinning and drawing under suitable conditions, a high tenacity which is of the order of 8-l0 g.p.d. at extensions of lO-l4% but their shrinkage properties for example at 150 C. are such as to result in a l0l4% free shrinkage, and shrinkage force of 0.55 g.p.d.

In order to reduce this shrinkage various heat treatments are known such as hot ovens, passage over hot plates, but under these conditions other properties such as tenacity, elongation and modulus are undesirably reduced.

We now provide a process for the treatment of these high tenacity filaments without appreciably affecting other properties, in which the heat treatment is carried out at very high and accurately controlled conditions.

According to our invention therefore we provide oriented crystalline filaments made from polyethylene terephthalate in which the intrinsic vi:cosity of the polymer is 0.85l.0 (11. per gram and which have uniform properties throughout their length with at least 8 g.p.d. in the form of a yarn of up to 10,000 denier and not more than one turn per inch twist, an extension of at least 10%, a shrinkage of less than 8%, a 2% modulus of at least 90 g.p.d. and a shrinkage force at 150 C. of less than 0.35 g.p.d.

The tensile properties referred to herein are as determined on an Instron Tensile Tester with a guage length of 30 mm. and a cross head speed of 10 cm./min. The shrinkage referred to is the free shrinkage of yarn samples after mins. in air at 150 C. The shrinkage force is as determined in silicone oil at 150 C.

The intrinsic viscosity is determined in the usual manner by dissolving yarn samples in orthochlorophenol and measuring the fiow times of a 1% solution of the sample, and of the solvent, in a suitable Ostwald viscometer at C. (As described in ICI Fibres Limited Technical Information Manual, Section C.2.)

We also provide a process for making such high tenacity filaments from polyethylene terephthalate in which the intrinsic viscosity of the polymer is 0.85l.00 dl. per gram, comprising positively passing filament yarns of up to nited States Patent 0 3,413,797 Patented Dec. 3, 1968 10,000 denier with not more than one turn per inch twist between feed means to takeup or winding means rotating at predetermined relative speeds, which may be the same or slower, wherein the filaments are passed through a heating zone for a time between 1 and 12 secs., the heating zone being equipped with positive heat exchange means comprising a multitude of solid particles maintained precisely at a temperature or 3 C. in the range 240- 264 C. that is to say 25-1 C. below the melting temperature of the filaments.

In one embodiment of our invention the filaments are relaxed 34% while passing through the heating zone at speeds of at least 300 metres per minute, preferably 1,000 metres per minute using treating times of the order of 2-5 seconds. In order to achieve the required treating times a multiple path through a single heating zone may be used in one bath or several baths may be used in series. The tension in the heating zone may be controlled by the relative diameters of Godet wheels or by adjusting relative speeds of wheels of identical diameter or by a combination of diameter and speed of the wheels or of rolls.

The filament yarns when relaxed as hereinbefore described are eminently suitable for fabrics which are to be coated, for example with PVC or neoprene.

In another embodiment of our invention the filaments are kept at constant length whilst passing through the heating zone at speeds of at least 300 metres per minute preferably 1,000 metres per minute using treating times of the order of 52 seconds, as described above. Filament yarns heat treated at constant length have high modulus and tenacity required in rubber reinforcements particularly V-belts, conveyor belts, tyres and hose such as fuel conveying hose.

The positive heat exchange means which are suitable and as far as is known to us at present the only suitable means, comprise a multitude of solid particles which are brought into intimate contact with the filaments and which are heated to the required temperature in a suitable bed for the particles, without melting or substantially affecting other of their properties. The filaments, which may be preheated are passed near to or through the bed of the solid heated particles, before being brought into contact with the solid particles. The multitude of solid particles may be maintained in a fluidised condition by a gas stream which is heated and maintained at the required temperature. The required temperature may be maintained by heating the particles in a bed of the particles and the gas stream itself may also be heated during or before passage through the bed of particles.

In our process the particles may be heated in a suitable container which is provided with inlet means for the gas, or the gas may be introduced by an upward-pointing pipe without actually passing through the wall of the container. When the gas is turned on, the particles are propelled upwards and maintained in motion by the interaction of the gravity of the particles and the upsurging gas stream or streams.

In another form of the process the particles may be brought to the required temperature in a suitable bed and metered by gravity downwards onto the filaments. In this form, means are required for bringing the particles back into the bed. Mechanical conveyor means or arr or gas conveyors are suitable.

If the particles are maintained in a fluidised condition by an upwards surging gas or air stream, a bed of SOlld particles is provided and the particles are kept in suspension by the velocity of the gas and the particles behave like a liquid so that objects which would remain on the surface of the solid particle bed when it is not kept in suspension by the gas stream, will sink rapidly into the bed of particles when they are held in suspension by the gas stream. Such fluidised particles effect a rapid transfer of heat to objects immersed therein.

Suitable positive heat exchange means comprise a bed of fluidised solid particles which are fluidised and heated by means of a gaseous current and heated e.g. electrically. By a fluidised solid we denote small solid particles which are suspended or kept in suspension in a current of gas which may be passed through the particles in such quantities and speed that the particles may be held in suspension or move about freely.

A bed of solid particles which are kept in suspension by the velocity of the gas behave like a liquid and objects which would remain on the surface of the solid particle bed when it is not kept in suspension by the gas stream, will sink rapidly into the bed of particles when these are held in suspension by the gas stream.

Suitable solid particles which may be used for carrying out our heat treatment comprise sand, glass, ballotini, small aluminium spheres and other solid materials which are or can be suitably graded preferably to a fairly uniform size.

Particles having a diameter or cross-section of about 1 mm. but not below 50 microns are suitable. The particles can be heated by means of coils immersed in a bed of such particles or by circulating heating fluids through a suitable jacket around a container in which the particles are situated. They can also be heated by electrically heated elements which are immersed in the particles, or which form the walls of the container or by other means for heating the walls of the container for the solid particles.

The vessel containing the bed of solid particles may be provided with means for injecting or circulating the current of gas, vapour or air at the desired rate to keep the solid particles in suspension.

The filaments are passed through the fluidised bed at constant length, or with relaxation or stretch depending on the balance of properties required in the product. The dwell time, depending on denier, may vary preferably between 1 and 12 seconds as already stated. For 1,000

viscosity in the range 0.85 l.0 dl./g. heat setting at constant length at these temperatures does not reduce free shrinkage and the shrinkage force, (at 150 C.) to the required level. In order to reduce the shrinkage properties of our high intrinsic viscosity yarns we have found that they must either be heat-set at constant length at temperatures above 240 C. or be heat-relaxed 3 to 4% at the stated temperatures of 240264 C.

If low shrinkage properties are more important than yarn modulus, the heat relaxation process is to be preferred. If yarn modulus is more important, then heatsetting at constant lengths is preferable. In both cases heat-setting at the stated highest possible setting temperature gives the best result. As far as is known only positive heat-exchange with the multiude of solid particles preferably by the fluidised bed process, allows sufiicient temperature control to operate at the required heat setting temperature within 24-1 degree of the yarn M.P. in a commercially acceptable manner. In the case of polyester yarn with intrinsic viscosity in the range 0.89-1.0 d1./g., it is therefore necessary to use the fluidised bed process in order to obtain satisfactory shrinkage properties for commercial operations.

The following examples illustrate preferred embodiments of our invention.

EXAMPLE 1 A sample of 1,000 denier T erylene polyethylene terephthalate t.p.i. S twist filament yarn of I.V. 0.90 dl./"g.. tenacity 8.5 g.p.d. and 10.1% extension was heat set at constant length through a fluidised bed under the following conditions.

Threadline speed yd./min 600 Number of wraps 16 Number of beds 1 Time in bed sec 2.6 Applied stretch percent 1) The effect of the heat setting treatment on the yarn physical properties was as follows.

Yarn Physical Property Bed Temperature, Breaking Exten- 2% 150 0. 150 0.

C. Denier Strength Tenacity sibility Modulus Free Shrinkage (1b.) (g.p.d.) (percent) (g.p.d.) Shrinkage Force (percent) (g.p.d.)

denier yarn a dwell time of 1-5 seconds, preferably 2.53.5 seconds, is suitable. Path lengths through the hot zone may be varied by adjusting the number of passes, i.e. number of wraps round a pulley system in a single bed, or by using a number of beds in series.

an extra-high tenacity polyester yarns, having an intrinsic 6 Example 1 also shows that free shrinkage does not decerase below 8% until temperature exceeds 240 C. Neither does shrinkage force approach the satisfactory level of 0.30 g.p.d. In this example, constant length heat setting, no loss of modulus occurs, above 240 C.

In the case of tyre, V-belts etc. it is important that the textile reinforcement does not shrink execessively during rubber vulcanisation, as distortion and loss of modulus takes place. In these applications the shrinkage properties have to be reduced to a minimum while at the same time retaining textile modulus and strength. It will be seen from Example 1 that this is best achieved at the highest temperatures.

EXAMPLE 2 As Example 1 but using 3% relaxation.

Yarn Physical Property Bod 'lmupcraturc, Breaking Exton- 2% 0. 150 C.

C. Denier Strength Tenacity sibility Modulus Free Shrinkage (1b.) (g.p.d.) (percent) (g.p.d.) Shrinkage Force (percent) (g.p.d.)

Unset yarn 1, 002 19. 4 8. 5 10. 1 82 13. 0 0. 55 220i1 1, 068 19. 7 8.4 14. 2 66 5. 9 0. 16 24055. 1, 036 19. 1 8. 4 14. 5 68 5. 4 0. 14 20011 1, 059 18. 2 7. 8 14. 3 G8 4. 6 0, 13

In the manufacture of coated fabrics it is very important that the yarns comprising the base fabric should have low and consistent free shrinkage at the temperature reading in curing the elastomer coating (120-190 C.). If this is not the case cockling of the fabric will occur preventing an even coating of elastomer to be obtained. The requirement for very consistent shrinkage overrides the requirement for high modulus and tensile strength in this end use.

It will be seen in Example 2 that 3% relaxation results in lower free shrinkage and much lower shrinkage force than constant length heat setting (Example 1) but at the expense of yarn modulus. The variability of free shrinkage is also extremely small in this fluidised bed process being of the order of 5i0.5%. This makes the relaxed yarn very suitable for use in coated fabrics.

What I claim is:

1. Oriented crystalline filaments made from polyethylene terephthalate in which the intrinsic viscosity of the polymer is 0.851.00 d1. per gram and which have uniform properties throughout their length with at least 8 g.p.d. in the form of a yarn of up to 10,000 denier and not more than two turns per inch twist, an extension of at least 10% and a shrinkage of less than 8% and a 2% modulus of at least 80 g.p.d. and a shrinkage force of less than 0.35 g.p.d.

2. Oriented crystalline filaments made from polyethylene terephthalate according to claim 1 in the form of rubber reinforcements.

3. Oriented crystalline filaments made from polyethylene terephthalate in which the intrinsic viscosity of the polymer is 0.851.00dl. per gram and which have uniform properties throughout their length with at least 8 g.p.d. in the form of a yarn of up to 10,000 denier and not more than two turns per inch twist, an extension of at least 10% and a 2% modulus of at least 65 g.p.d. when the shrinkage is 5:0.5% and the shrinkage force less than 0.15 g.p.d.

References Cited UNITED STATES PATENTS P FRANK J. COHEN, Primary Examiner. 1)

W. H. SCHROEDER, Assistant Examiner. 

